Alarm



A. H. LAMB Sept. 15, 1936.

ALARM Filed Oct. 27, 1932 3mm; awe; 16M,

Patented Sept. 15, 1936 v a I UNITED STATES PATENT OFFICE ALARM Anthony H. Lamb,'Elizabeth, N. J., assignor to Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New York Application October 27, 1932, Serial N0. 639,923 a a 1 Claim. (01. 177-311) This invention relates to an alarm for indicatnected to the relay terminals 6, I, and 'I', reing critical light intensities and particularly to a spectively. photoelectrically controlled alarm. The terminals 6 and 1 are connected to are- It is very desirable that warning of critical light tarding thermal relay or switch 8, the connecting conditions such as the advent of excessive or incircuit including a source of current such as the adequate light begiven automatically so that steps secondary 9 of a step-down transformer l0 that may be taken to produce, artificially, a normal has its primary H connected across the customary light. It is an-accepted fact that working in H0 volt power or light line. The retarding relay8 semi-darkness, or light of brilliant intensity, not includes a bimetallic strip l2 supported at I3 and 1 only severely strains the eye muscles but also cona heating coil it for the strip, the strip flexing tributes to general loss of health, both of which with changes in temperature to move its contact result in lowered efliciency of the worker. i5 toward and away from the relatively fixed Unfortunately, the eye itself does not give warncontact I6. To prevent variation of the delay ing of dangerous changes in illumination but period with changes in the atmospheric temadapts itself to slow changes and it is not until perature, the contact I6 is moimted on a bimetal- 15 other parts of the body give warning that a lic strip I6 that hasthe same temperature charworker notices the changes, so that, without some acteristic as the contact strip l2. warning, it very frequently happens that lights The contact I6 is connected to one terminal of are not switched on to increase illumination or the alarm H, the other terminal of which is conshades drawn to decrease it until the damage has nected to one side of the power supply. In order 20 been done. to complete the alarm circuit, the fixed end B of It is, therefore, an object of this invention to the strip I2 is connected by a conductor l8 to the provide an alarm automatically responsive to other side of the power supply. critical changes in the intensity of light. The relatively fixed contacts 5, 5 are so ad- Another object of this invention is to provide justed that, with normal illumination, the our- 25 an alarm automatically responsive to inadequate rent flow established in coil 2 by the cell I will light conditions. position the contact arm 4 in the gap between A further object of this invention is to provide the fixed contacts. When the illumination dean alarm automatically responsive to excessive parts from the desired or normal values range,

light conditions. the current flow established in coil 2 is such that 30 A still further object of the invention is to prothe contact arm 4 engages one of the contacts, vide an alarm automatically responsive to the say the contact 5 in the case of excess illuminacritical light intensities in which a neon lamp or tion. The circuit is thus closed through the curcombinations of a plurality of neon lamps give rent source 9 and the heating coil, but the circuit the indication. to the alarm of signal I1 is not immediately 35 These and other objects will be apparent when closed, as premature or repeated signals corretaken with the accompanying drawing, in which: sponding to momentary fluctuations in illumina- Fig. 1 illustrates diagrammatically a system in tion are to be avoided. The heating coil of the which a single indicating device provides the delay switch 8 must be energized for a predeteralarm, and mined time interval before the alarm circuit is 40 Fig. 2 illustrates diagrammatically a system in closed to afford an indication that the illuminawhich combinations of a plurality of indicating tion has definitely passed above the critical value. devices provide difierent alarms for different pre- It will be apparent that the heating coil circuit determined light conditions. could be connected to the lower current contact Referring to Fig. 1, the reference numeral l 5' to provide an alarm when the illumination 45 indicates alight sensitive alarm such as aphotofalls below the normal range of values, or a electric cell or photocell which is placed at the thermal delay switch and signal could be duplipoint at which the illumination or light intensity cated to provide an alarm when the illumination is to control the operation of the alarm. The changes to either less or more than normal.

cell or cells I is or are connected to the moving Preferably, however, such a double alarm sys- 50 coil 2 of the sensitive relay 3, the movable coil tem will be arranged as shownin Fig. 2 toprovide having a contact 4 movable between two a. series of significant signals that are closely relatively fixed contacts 5. 5' in accordance with and directly related to their corresponding ranges the current flow established in the coil. The of illumination. movable arm 4 and the contacts 5, 5' are con- In the alarm system oi. Fig. 2, a number of the circuit elements may be substantially identical with those shown in Fig. 1, and such elements are identified by their corresponding reference numerals but will not be described in detail.

In addition to the thermal switch 8 which is connected across the terminals 6 and i, of the sensitive relay 3, a second thermal switch I9 is employed for controlling the current flow to an alarm or signal 20. This switch includes a bimetallic strip 2! and heating coil 22, the design being generally the same as that of switch 8 but the strip is so arranged that its contact 23 is engaged with the relatively fixed contact 24 at normal temperatures. One end of the heating coil 22 is connected to the terminal I of the back contact 5', and the other end of the heating coil 22 is connected to the bimetallic strip 2| which, in turn, is connected to that side of the secondary winding 9 which is not connected to the center terminal 6 of the relay 3. The alarms or signals i1, 20 may be of any desired style, such as lamps, bells or the like, but are preferably neon lamps of different colors. The alarm 20 may be a neon lamp that is so colored as to produce a white or yellow light, while the alarm I 1 may be the usual neon lamp which gives a reddish glow.

With low or less than normal illumination, the

current flow produced in coil 2 by the cell l is not sufilcient to move the relay arm t from the contact 5', and current flows from the transformer secondary 9, through the heating coil 22, to open the contacts 23, 25, thus interrupting current flow through the alarm 20.

Within the range of normal illumination, the arm 4 does not engage with either of the contacts 5, 5 and therefore no current flows through either heating coil. Under these conditions, the switch l9 closes and the lamp 20 is lighted. With excess illumination, the larger current output of cell i closes contacts 4, 5 and current is supplied to the heating coil l4, and the contacts l5, it are thereby engaged, thus lighting the second lamp II. The signals displayed by the system are thus directly related to the illumination, i. e., no light is displayed when the illumination is low,

a single white light shows when the illumination is normal, and both the white and red lights show when the illumination is above normal.

Visual signals are, in general, to be preferred to audible signals since it would be necessary to provide additional manually controlled switches for opening the alarm circuits upon their closure by the cell, and a failure to reclose the manual switches when the illumination was again normal would render the system inoperative. Neon lamps are well adapted for this use since they draw but little current and may be operated from the usual power and light circuits.

I claim:

In a device for indicating illumination values, a pair of terminals for connection to a source of alternating current,a photocell and a relay haying two spaced contacts and a contact arm movable therebetween and actuated by said photocell in response to variations in the intensity of illumination values, a transformer, the primary of said transformerbeing connected to the said terminals, a pair of signal circuits each including a lamp, a pair of thermal switches each including an operating coil and a pair of contacts, circuit means for connecting the secondary of said transformer to said operating coils and the contacts of said relay, one of said coils being in circuit with one of said relay contacts and the other in circuit with the other relay contact, circuit means for connecting each lamp to the said terminals including the contacts of one of said thermal switches, one of said switches being normally open and the other being normally closed, whereby movement of said contact arm against one of said contacts will result in lighting of both lamps, movement to neutral position will result in extinguishment of one lamp and movement against the other contact will result in extinguishment of the other lamp, said thermal switches providing a time delay between the operation of said relay and a corresponding change in said signal circuits to prevent momentary fluctuations in illumination values from causing a change in the signal given.

ANTHONY H. LAMB. 

